摘要:全球氮沉降速率的急剧增加已显著地改变了生态系统的生产力及稳定性，特别是在受N限制较严重的亚高山草地生态系统。虽然氮沉降增加对草地生产力和植物多样性影响的研究报道已经很多，但是氮素沉降的生态系效应因气候区、草地系统类型、加氮水平、氮肥类型和试验时间长短等不同而差别很大。为了评估氮沉降增加对亚高山草地植物物种多样性和生产力的影响，通过在祁连山中部亚高山草地设置不同氮添加水平（0、2、5、10、15、25 g N m^-2 a^-1和50 g N m^-2 a^-1）的短期氮沉降增加模拟试验，探讨了生产力和物种多样性对不同水平氮添加的响应。结果显示：氮添加增加了禾本科（垂穗披碱草、赖草和草地早熟禾）和莎草科（矮嵩草）的地上生产力及其在群落生产力中所占的比例，主要表现在氮添加增加了禾本科和莎草科的株高和株数，降低了其他科（鹅绒委陵菜和葛缕子）的株高和株数；与生产力相比，植物多样性对氮添加的响应较慢，总体随着氮添加量的增加呈下降趋势但未达到显著水平；植物多样性与生产力呈显著的负相关关系。研究结果表明氮添加有助于提高禾本科和莎草科的生产力，进而提高群落生产力，但其他科的植物会被逐渐替代，导致群落植物物种多样性降低。研究结果可为我国亚高山草地的持续性管理提供一定的理论基础。



Abstract:Global atmospheric nitrogen deposition has increased steadily since the 20th century, and has significantly changed the stability and productivity of terrestrial ecosystems, especially in the N-limited alpine grassland ecosystems. Although there have been many research reports on the effects of increased nitrogen deposition on grassland productivity and plant diversity, the ecosystem effects of nitrogen deposition varied depending on the climate zones, grassland types, nitrogen addition levels, nitrogen types and experiment duration. In this study, we manipulated the rates of nitrogen addition (0, 2, 5, 10, 15, 25, and 50 g N m^-2 a^-1) in an subalpine grassland in Qilian Mountains, China, between 2018 and 2019, and assessed the effect of the short-term simulated nitrogen deposition on plant species diversity and productivity. The results showed that nitrogen addition significantly increased the aboveground productivity of Gramineae (Elymus nutans, Leymus secalinus and Poa pratensis) and Cyperaceae (Kobresia humilis) and their proportion of the aboveground productivity in the community, which was mainly manifested in the significantly increased plant height and number of Gramineae and Cyperaceae with nitrogen addition. Compared to the Gramineae and Cyperaceae, nitrogen addition decreased the plant height and number for other families (Potentilla anserine and Carum carvi). In addition, the response of plant diversity to nitrogen addition was much slower than the response of the primary productivity, and the plant diversity generally decreased as the nitrogen addition rates increasing, although the decreased trend was not significant. Moreover, we found a significantly negative correlation between plant diversity and their productivity. These results showed that nitrogen addition could improve the productivity of both Gramineae and Cyperaceae, which subsequently improving the community productivity, whereas other families would be excluded gradually, leading to the loss of plant species diversity. Our results provide a synthetic understanding of the effects of simulated nitrogen deposition on plant species diversity and productivity in alpine grassland, as well as the theoretical basis for the sustainable management in subalpine Grassland in China.





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